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Flexible Carbon Nanotube-Epitaxially Grown Nanocrystals for Micro-Thermoelectric Modules
No full textFlexible thermoelectric materials have attracted increasing interest because of their potential use in thermal energy harvesting and high-spatial-resolution thermal management. However, a high-performance flexible micro-thermoelectric device (TED) compatible with the microelectronics fabrication process has not yet been developed. Here a universal epitaxial growth strategy is reported guided by 1D van der Waals-coupling, to fabricate freestanding and flexible hybrids comprised of single-wall carbon nanotubes and ordered (Bi,Sb)(2)Te-3 nanocrystals. High power factors ranging from approximate to 1680 to approximate to 1020 mu W m(-1) K(-2 )in the temperature range of 300-480 K, combined with a low thermal conductivity yield a high average figure of merit of approximate to 0.81. The fabricated flexible micro-TED module consisting of two p-n couples of freestanding thermoelectric hybrids has an unprecedented open circuit voltage of approximate to 22.7 mV and a power density of approximate to 0.36 W cm(-2) under approximate to 30 K temperature difference, and a net cooling temperature of approximate to 22.4 K and a heat absorption density of approximate to 92.5 W cm(-2)
When Is Depreciation Meaningful in Valuation? Changing Valuation Weights for U.S. REITs and Non-REITs?
No full textThis article regresses the market value of equity on pre-depreciation income and on depreciation expense for capital-intensive firms, referring to the coefficients from our model as valuation weights. The valuation weight on depreciation expense versus the weight on pre-depreciation income are compared, to detect depreciation biases, over time and across sectors. Our model shows that the valuation weights on depreciation expense change over time, if the persistence of the cash flow components of net income varies over time and if the accrual for depreciation is inflexible (e.g., straight-line depreciation). For Real Estate Investment Trusts (REITs), we find the valuation weight on pre-depreciation income increases with industry upturns, while the valuation weight on depreciation expense decreases during upturns. This result is contrasted to the nearly equal valuation weights for the cash flow and depreciation components of earnings for Resource firms (e.g., mines) over time. We conjecture this is because depletion accounting flexibly allows for ???depreciation??? to exhibit less bias than in other sectors. In summary, actual depreciation practices influence time variation in the valuation of depreciation, a point which has been underappreciated in prior studies
Recent Advances in Solution-processed Inorganic Thermoelectric Thin Films
No full textRecent advancements in microscale electronics and wearable devices have led to the concept of energy autonomy, which requires self-powered energy sources that can be integrated into systems. Thermoelectric generators have received significant attention as direct energy conversion systems between heat and electrical energy. However, typical bulk-scale inorganic thermoelectric materials have limited utility in these systems, and the traditional fabrication methods of generators pose difficulty in their miniaturization. Thin-film thermoelectric materials can address these issues owing to their easy integration into microscale systems. Moreover, solution processing can provide a cost-effective and scalable production approach for inorganic thin films. In this paper, we review the recent progress in solution-processed inorganic thermoelectric thin films, including the synthesis of ink solutions, fabrication of thin films, and thermoelectric performance of materials and devices
High enrichment and near real-time quantification of airborne viruses using a wet-paper-based electrochemical immunosensor under an electrostatic field
No full textConventional airborne virus measurement usually requires appreciable sampling and detection times. Viral aerosols should also be collected or prepared in a liquid medium whose volume typically ranges from milliliters to tens of milliliters; hence, many sampling and detection steps need to be taken with the unit horizontal or immobile. Moreover, viral aerosols need to be sufficiently enriched, which makes real-time monitoring difficult. Herein, we present a near real-time enrichment and quantification system of airborne viruses that consists of a wet-paper-based electrochemical immunosensor with a gel electrolyte and a modified electrostatic particle concentrator. A small amount of phosphate-buffered saline flowed on the electrode, which resulted in sensor electrodes that are barely wet (covered in a thin buffer film measuring several micrometers) to ensure antigen???antibody interaction and the removal of non-target particles on the electrode surface. This system ensures that airborne viruses are highly enriched on the working electrode of the immunosensor, and it is possible to measure the MS2 virus particle concentrations every 10 min for 60 min stably and selectively against non-target airborne viruses and bacteria at horizontal and tilted measurement configurations. This system thus has the potential to be used in the real-time mobile monitoring of airborne microorganisms
Chain rotational dynamics in dilute polymer solutions and melts under shear flow
No full textWe present detailed scaling characteristics of the chain rotation dynamics in shear flow for melt and dilute linear polymer systems using extensive atomistic and coarse-grained Brownian dynamics (BD) molecular dynamics simulations, respectively. We find that the dilute systems with hydrodynamic interaction (HI) and excluded volume (EV) effects generally exhibit two distinct scaling behavior of the chain rotation time ??rot between the intermediate and strong flow regimes, whereas the free-draining dilute polymer systems display a relatively simple single-scaling behavior for ??rot with respect to the shear rate throughout the intermediate-to-strong flow regimes. This dynamic feature correlates with the scaling characteristics of average chain deformation and orientation of the system with respect to the flow strength. Notably, the combined HI and EV effects generally weaken the structural change of polymer chains in response to the applied flow and enhance the overall chain rotation dynamics by disturbing the chain stretch and alignment to the flow direction. Accordingly, due to the variation in the HI and EV effects (in association with chain deformation) with the flow strength, the dilute systems with HI and EV turn out to reveal relatively lower and higher scaling behaviors of ??rot in the intermediate and strong flow regimes, respectively, in comparison to the corresponding free-draining systems. Despite the absence of HI and EV effects, the melt systems also exhibit two distinct scaling behaviors of ??rot between the intermediate and strong flow regimes. This feature arises from the intermolecular interactions between chains, resulting in a significant influence of interchain entanglement and interchain dynamic collision on the chain rotation dynamics. It is further observed that the overall ??rot scaling behavior for each system is predominantly determined by the corresponding scaling behavior of the kinematically stable (diffusive) angular regions near the flow direction, where the flow force is relatively weak. Additionally, polymer chains in kinematically unstable (convective) angular regions exhibit nearly affine chain rotation dynamics conforming to the imposed flow field, independent of the polymer concentration and chain length. This is considered to be a universal feature for general polymeric liquids in shear flow
Naphthalene diimide-based random terpolymers with axisymmetric and asymmetric electron acceptors for controllable morphology and enhanced fill factors in all-polymer solar cells
No full textAll-polymer solar cells (all-PSCs), based on p-type polymer donors and n-type acceptors as the active layer, offer exceptional promise because of excellent thermal stability, superior film formation, and good mechanical stress as a unique bulk heterojunction (BHJ) solar cell combination. Therefore, tuning the molecular composition between polymers is crucial for optimizing power conversion efficiency (PCE) in these all-PSC systems. In this study, we synthesized a series of naphthalene diimide (NDI)-based random terpolymers P(NDI-BDD10), P(NDI-TPD10), P(NDI-TT10), and P(NDI-2FQ10) with axisymmetric (BDD, TPD) and asymmetric (TT, 2FQ) electron acceptors. Compared with the blend morphology of PBDB-T:N2200, their diverse effects due to the addition of trace amounts of axisymmetric and asymmetric components were comprehensively investigated using physical and surface analyses and structural simulations. Consequently, most of our polymer acceptors demonstrated improved fill factors (FFs) in the optimal morphology. P(NDI-BDD10)-based devices achieved the highest PCE of 6.80% and FF of 69.1%, while the architecturally most asymmetric P(NDI-TT10)-based devices reached the lowest PCE of 4.52% despite an enhanced FF of 65.4%. As a result, the appropriate molecular arrangement is crucial for obtaining the desired morphology and improved PCE. Our findings give novel molecular design insight into the distinctions between axisymmetric and asymmetric electron acceptors and seem significant for achieving improved morphological features and efficiency
Moduli of Fontaine--Laffaille representations and a mod-p local-global compatibility result
No full textImportance of broken geometric symmetry of single-atom Pt sites for efficient electrocatalysis
No full textPlatinum single-atom catalysts hold promise as a new frontier in heterogeneous electrocatalysis. However, the exact chemical nature of active Pt sites is highly elusive, arousing many hypotheses to compensate for the significant discrepancies between experiments and theories. Here, we identify the stabilization of low-coordinated Pt-II species on carbon-based Pt single-atom catalysts, which have rarely been found as reaction intermediates of homogeneous Pt-II catalysts but have often been proposed as catalytic sites for Pt single-atom catalysts from theory. Advanced online spectroscopic studies reveal multiple identities of Pt-II moieties on the single-atom catalysts beyond ideally four-coordinated Pt-II-N-4. Notably, decreasing Pt content to 0.15 wt.% enables the differentiation of low-coordinated Pt-II species from the four-coordinated ones, demonstrating their critical role in the chlorine evolution reaction. This study may afford general guidelines for achieving a high electrocatalytic performance of carbon-based single-atom catalysts based on other d(8) metal ions. Electrochemical CO2 conversion to methane offers a promising solution for the large-scale storage of renewable electricity, yet the catalytic selectivity at high current density still needs to be refined. Here the authors report to use both dissolved CO2 and in-situ generated CO2 from bicarbonate to sustain high local CO2 concentration around Cu electrode and thus achieve selective CO2 conversion to methane
Detecting and Characterizing Young Quasars. III. The Impact of Gravitational Lensing Magnification
No full textWe test the impact of gravitational lensing on the lifetime estimates of seven high-redshift quasars at redshift z greater than or similar to 6. The targeted quasars are identified by their small observed proximity zone sizes, which indicate extremely short quasar lifetimes (t ( Q ) less than or similar to 10(5)yr). However, these estimates of quasar lifetimes rely on the assumption that the observed luminosities of the quasars are intrinsic and not magnified by gravitational lensing, which would bias the lifetime estimates toward younger ages. In order to test the possible effects of gravitational lensing, we obtain high-resolution images of the seven quasars with the Hubble Space Telescope and look for signs of strong lensing. We do not find any evidence of strong lensing, i.e., all quasars are well described by point sources, and no foreground lensing galaxy is detected. We estimate that the strong-lensing probabilities for these quasars are extremely small (similar to 1.4 x 10(-5)) and show that weak lensing changes the estimated quasar lifetimes by only less than or similar to 0.2 dex. We thus confirm that the short lifetimes of these quasars are intrinsic. The existence of young quasars indicates a high obscured fraction, radiatively inefficient accretion, and/or flickering lightcurves for high-redshift quasars. We further discuss the impact of lensing magnification on measurements of black hole masses and Eddington ratios of quasars
